The human T cell antigen receptor (Ti) has recently been identified as a 90KD T3- associated clonotypic structure composed of one 49-51KD Alpha and one 43KD Beta subunit which are disulfide linked. Monoclonal antibodies to the Ti structure of a given clone inhibit all of its antigen specific function. In contrast, Sepharose-bound anti-Ti antibodies which are capable of crosslinking the T cell receptor possess antigen-like effects. Direct biochemical comparison of Ti molecules from antigen specific clones derived from the same donor but of differing specificities has demonstrated that the Alpha and beta subunits bear no precursor-product relationship to one another and are unique for the given clone. However, in addition to the Ti structure, the T3, T4 and T8 glycoproteins are involved in antigen recognition by human T lymphocytes. To understand the molecular basis of T cell receptor specificity and diversity, the following proposal will address three areas: 1) molecular cloning and analysis of the Ti alpha and Ti beta genes; 2) molecular cloning of T3, T4 and T8; and 3) gene transfer experiments to alter T cell specificity for nominal antigen and/or MHC restricting element. Firstly, Ti alpha and Beta genes will be identified using oligonucleotide probes generated from amino acid sequences of purified subunits either to directly screen a cDNA library or primer extend prior to screening. Once identified, cDNA clones will be sequenced, sublconed and the latter used to determine whether variable and constant domains exist in these Ti subunits and for analysis of possible Ti alpha and beta gene rearrangement during differentiation. Subsequently, by screening a large panel of regulatory and effector T cell clones, it will be possible to determine whether isotypic domains exist within the Ti structure. Genomic Lambda phage libraries will be utilized, in addition, to determine the precise structure of these genes and their relationship to immunoglobulin genes as well as to performing chromosome localization studies. Secondly, T3, T4 and T8 genes will be defined by molecular cloning and T lineage differentiation characterized with respect to transcriptional activity of these genes in human thymus. Thirdly, employing protoplast fusion and calcium phosphate transfection, Ti alpha and beta genes will be inserted into other T cells to determine whether one can alter T lymphocyte specificity for nominal antigen and/or MHC restricting elements. The contribution of T4 and T8 genes in this recognition process will also be determined.